Clinical manifestations of Lyme disease include vasculopathies in neural, cardiac, synovial, and dermal tissue, as well as marked perivascular infiltration of leukocytes. Moreover, the early stages of Lyme disease are accompanied by increases in the permeability of the vasculature of the central nervous system. Since at least some of these derangements occur within 24 to 48 hours after infection, it seems likely that Borrelia burgdorferi, the causative organism of Lyme disease, contributes to their pathogenesis by mechanisms that are independent of a host immune response. These mechanisms may involve direct effects of B. burgdorferi on leukocytes or vascular endothelium of the infected host, or they may involve disturbances of the normal interactions between these two host cell types. This hypothesis will be examined using in vitro models, which will allow examination of the interactions between cells in a more controlled, quantitative fashion than is possible in vivo. Purified human neutrophils, monocytes, lymphocytes, and natural killer cells, as well as monolayers of endothelium cultured from human umbilical vein, will be used to pursue the following specific aims: 1) To investigate the production by B. burgdorferi of factors that are chemotactic for leukocytes. 2) To determine whether the permeability properties of endothelial monolayers are affected by B. burgdorferi. Permeability to both macromolecules and ions will be assessed. 3) To determine whether endothelium is "activated" in response to B. burgdorferi. Activation is characterized by upregulation of adhesion molecules for leukocytes, increased expression of MHC Class I and Class II antigens, increased rates of synthesis of macromolecules, and hypertrophy of the endothelial cells. 4) To investigate changes in leukocyte adhesion to and migration across endothelium after the endothelium has been exposed to B. burgdorferi. The roles of adhesive molecules on the endothelial cell surface in mediating these changes will be determined. A long-range goal of this project will be to identify spirochetal components that are responsible for observed effects of B. burgdorferi on leukocytes or endothelium. It is anticipated that these studies will contribute to understanding the origins of vascular damage and inflammatory infiltrates not only in Lyme disease, but in other bacterial infections as well.